1. Enzymes are biological or protein catalysts.
What is a catalyst?
A substance that speeds up a reaction without being changed by the reaction.
Enzymes are biological or protein catalysts.

2. Exothermic and Endothermic Reactions
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3. Endothermic and exothermic reactions
Step 1: Energy must be SUPPLIED to break chemical bonds:
Step 2: Energy is RELEASED when new chemical bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED. If more energy is SUPPLIED than is RELEASED then the reaction is ENDOTHERMIC
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4. Energy level diagrams Energy level Activation energy
Using a catalyst might lower the activation energy
Energy given out by reaction
Reaction progress
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5. Forming Na+ and Cl- ions from NaCl is an endothermic process
Endothermic process: a change (e.g. a chemical reaction) that requires (or absorbs) heat.
Forming Na+ and Cl- ions from NaCl is an endothermic process
Photosynthesis is an endothermic reaction (requires energy input from sun)

6. Measuring Heat
reaction
Endothermic reaction, heat taken in & temperature of the substance drops

7. Ammonium nitrate + water

8. Starting temperature 20⁰ C

9. Add ammonium nitrate to water

10. a temperature decrease of 8⁰ C

11. EXOTHERMIC & ENDOTHERMIC REACTIONS
Exothermic process: a change (e.g. a chemical reaction) that releases heat.
Burning fossil fuels is an exothermic reaction

12. Exothermic reaction, heat given off & temperature of substance rises.
Heat Released
reaction
Exothermic reaction, heat given off & temperature of substance rises.

13. Exothermic vs endothermic:
EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration)
ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)
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14. Examples Exothermic Combustion of fuels Yeast & Hydrogen Peroxide
Epson salts & water
Endothermic
Photosynthesis
Acedic Acid & Sodium Bicarbonate
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